4th Gear 35mph vibration/quiet thumping sound from middle-rear of truck 6 speed trans

Hi all, as of yesterday i've notice a weird vibration and odd thumping noise coming from somewhere in the rear drive-line of my truck, a 2012 DCSB 6 speed manual. this thump/vibe ONLY happens when the truck is in ONLY in 4th gear and ONLY at 35mph, it wont do it in 3rd gear or 5th gear at all weather its at 35mph or not, just in 4th gear, the truck only has 20,300 miles on it, driven extremely lightly only on-road and is always serviced at the right intervals, i service the U-joints every 5,xxx miles like the manual says to. the truck only has a 1.6 inch lift up front with toytec/eibach springs on 5100's (springs installed last week), nothing in the back except for the TSB leaf pack that was there from the factory and 5100's (my setup is very similar to that of a factory TX Baja). the truck was aligned after this job as well by the dealer. on a side note, i began feeling this thumping/vibe yesterday right after i took the truck on its first long highway journey, approx 200 miles, in a very long time, i dont really take the tacoma on long trips very often, and i felt it almost immediately after getting off the highway when again traveling in 4th at 35mph. these things are leading me to believe the carrier bearing may the culprit but i really dont know and am not sure, could it be a U-joint or something messed up internally in the transmission?? (also have not changed the transmission fluid yet, its still original, should i change it?? ) again, this thumping/vibe is very slight and only happens when cruising in 4th gear at exactly 35mph, its livable but just an annoyance since its there and the vibe can slightly be felt by my foot on the gas pedal... any help is appreciated, thank you.

BTW i know its a truck and not a refined audi or something, but this noise was never there before.

 

The 6spd has gears that low?

 

i suppose it does lol.. im no transmission expert lol... but yeah.. it cruises at about 35mph at approx 1.6k rpm nicely on a road that has a 40mph speed limit lol

 

Warranty Work! Take it back to the dealer.

Sound like it could be a universal join or center carrier bearing however.

 

Oh jeeze... dont tell me that... I cant stand bringing the truck to dealer. but ok, because thats what it feels like to me anyway.

 

Hahaha was just gonna say simliar Brock... Seems like to high a gear to be in at too low of a speed, the 6 speed maual always seemed to high geared to me, I'm thinking that it doesn't really care for that gear choice for that road speed...

 

That is logical thinking there, because as soon as I go a mile an hour or so faster it totally goes away lol

 

Bump??

 

Whatever the cause, it's too soon for a truck with only 20,000 miles. Taking it to the dealership sucks, but at least you still have a warranty.

 

So you really think I should take it to the dealer then.. ?? :/

 

Yes, if you want it fixed for free. It should be a quick job if it's just a bad center bearing or u-joint.

 

Alright, I may try to bring it in this week... damn this sucks, but you dont think it could be the transmission?? Because like I was saying, it only happens in 4th.... but like you said, it may be the carrier or u joint because I feel the thumping noise is coming from behind me more so then right near me which is where the transmission would be. I just dont understand why the noise would be 4th gear specific.

 

Dude, yer not getting it I think, I was being a little sarcastic , what i mentioned before IS the problem, you can't roll around in any manual (well , you CAN but) in 4th gear going 35mph & not expect some low rpm lugging anomalies, ask yourself this "What are my shift points?: 1st gear up to 15mph, shift, 2nd gear up to 25mph, shift, 3rd gear by the time you let out the clutch again & slightly accelerating, your going to be probably at or slightly over 35mph & still well below any noticeable raise in RPM range.... I can appreciate your concerns bro' but I think you're being a little too anal about , & at slightly over 20k I'd be absolutely flabbergasted & shocked if it were a Ujoint or especially a carrier... Now can it be one of those ??> Sure, but smart money says that its your driving style driving in too high of a gear at too low road speed & 1600 RPM at 35 isn't saying alot really, i go 65mph at around 1800 RPM on flat surface with good humidity but i digress, by your own admission you say it doesn't exist above or below 35mph in 4th gear, try shifting into 3rd at 19 or 20 mph while maintaining that RPM & see if you can replicate it in that gear.. How about tires ?? & you did say theres no lift in the back other than the TSB ?? & it was done before this noise appeared ?? Please understand I'm just trying to help ya, not berate ya...

 

Anything is possible, but the vast majority of auto repairs are for relatively simple problems. It is much more likely to be the driveline than a transmission on the verge of failure. A combination of a specific powertrain RPM with a specific ground speed causing noise/vibrations are classic symptoms of a driveline problem. Could be a u-joint, a center bearing, seized slip joint, or even a weight fell off the driveline and it's out of balance.

Even if it turns out to be transmission defect, you have a warranty so it will only be an inconvenient pain in the ass and not an EXPENSIVE inconvenient pain in the ass. For that I envy you...

 

Oh yeah man, believe me I appreciate everything you are trying to help me with honestly, and yeah, maybe it just is my driving style, idk, but the TSB springs were on there since the truck was conceived at the factory and ill have to try the 3rd gear thing, but the thing that boggles my mind is when I go into fifth at 35, seeing if that gear would do it just for haha's it does not, so go figure lol... but when id shift into 4th doing 40 mph it doesnt make any such vibration. And I usually don't go by speed for shift points, I go by rpm, and I usually shift into the next gear at about 2500 rpms or so. And plz, dont mind my ignorance, I 98% of the time dont get sarcasm lol

 

Yes, you are definitely correct in those aspects, but 4wd also has a good point that it is probably my driving style since I have such low miles, good maintance habits and such lite use, but I also definitely see your point the something could be defective because, lets face it, stranger things have happened.

 

Well I had my gf's father, who been a one man band mechanic for almost 30 years look at my truck and he said he didnt hear a thing, and he knows that I regularly and always maintain my truck all the time too, so he basically said im being too anal with it and theres no way its a u joint or carrier bearing or the trans. So yeah guess im being too picky

 

4th gear is NOT direct, 5th gear is (1.0). 4th is 1.19, 6th is .85.

 

oh crap, seriously?? ok then... well.... so hey, do you guys think that my recent 1.6 inch front leveling lift from the toytec coils could have caused this odd issue?? idk why it would because its an equivalent setup to the TX baja which is a factory setup, and according to tacomaHQ a 1.5 inch will not change the suspension geometry to where it would cause issues, and i still have about 3/4 to 1 inch of rake with the front lower than the back. any thoughts? thank you.

 

Brother... you are going to "anal" your truck right out of existience...